Method of making tube from strip metal stock



g- 1961 G. G. MALLY ET AL METHOD OF MAKING TUBE FROM STRIP METAL STUCK 2Sheets-Sheet l Filed March 5, 1958 INVENTORS LY, PETER LALLI GEORGE GMAL8; Zme mw GNIADOWSKI 5 M KM ATTORNEYS Aug. 29, 1961 G. G. MALLY ET ALMETHOD OF MAKING TUBE FROM STRIP METAL STUCK 2 Sheets-Sheet 2 FiledMarch 5, 1958 INVENTORS 650265 6. MALLY, PETER LALLI & ZBIGNIEWG-|Aoows| BY M M, Fad. (M

ATTORNEYS 2,998,047 METHOD OF MAKING TUBE FROM STRIP METAL STOCK GeorgeG. Mally, Peter Lalli, and Zbigniew Gniadowski,

Birmingham, Mich., assignors to Bundy Tubing Company, Detroit, Mich, acorporation of Michigan Filed Mar. 5, 1958, Ser. No. 719,416 9 Claims.(Cl. 15354) This invention relates to making tubing from strip metalstock and is especially concerned with the manufaoture of tubing havingwalls formed of a number of layers of stock.

United States Patent No. 2,292,810 to E. O. Woeller dated Angust 11,1942, discloses a method of fashioning metal strip stock transverselythrough about 720 while the strip is moving lengthwise to form tubinghaving twoply walls. Billions of feet of excellent tubing for hydraulicand other purposes have been made by use of the Woeller disclosure.However, the Woeller method gives rise to certain difliculties ofmanufacture which it is the object of the present invention toeliminate.

According to the Weoller method, a portion of the strip metal stock nearone edge is bent abruptly upwardly through about 90. The outer edge ofthe strip is then rolled or wrapped toward the bent up portion whichprovides a guide for the strip as it moves lengthwise and which supportsthe strip against the lateral forming pressure involved in rolling up orwrapping the strip. After the strip has been wrapped through about 1 /2turns the portions of the stock containing the abrupt L-shaped bend isironed out to provide this portion with a curvature approximately thatof the outer ply of the tube wall. The latter part of the stock is thenwrapped around the previously rolled up portion to complete the rollforming procedure per se.

During this process the portions of the strip which are first rolledthrough 1 /2 turns are stretched considerably more than the portionswhich are merely wrapped through about the remaining half turn aroundthe tube exterior. This results in uneven stresses tending to cause thetube to spiral and to twist on its longitudinal axis during subsequenttreatment such as when it is subjected to heat to bond the Wall pliestogether. Moreover, the portion which was first bent to L-shape and thenironed out is work hardened more than other portions of the tube, makingit difiicult to wrap the outer portion to complete the formation of thetube. In addition, the edge of the strip stock adjacent the abruptL-shaped bend is stretched to such an extent during formation of the Lthat it contains ripples downstream of the L-forming rolls which must besmoothed out by further rolling, thus work hardening this edge portionof the strip more than adjacent portions.

Heretofore, these and similar factors have necessitated passing thetubing over a mandrel and subjecting it to severe compressive forces toset the plies in contiguous relationship to prevent the tubing fromunwrapping and to prevent it from spiraling or twisting unduly afterleaving the tube mill. The tubing passes over the mandrel at the rate ofbetween 300 and 400 feet per minute. Various circumferential portions ofthe tubing are work hardened to materially different degrees.Consequently, wear on the mandrel is severe and uneven and the mandrelmust be frequently replaced, necessitating frequent tube mill stoppageswhich are expensive in mill hours production time lost, and in man hoursrequired for changing the mandrel.

The present invention provides a simple method of rolling tubing fromstrip stock which is improved to eliminate these disadvantages. Theinvention generally contemplates rolling longitudinal halves of thestrip trans- Patented Aug. 29, 1961 ice versely in opposite directionsin a generally symmetrical manner so that in wrapping the stock throughabout 720 each longitudinal half is wrapped through about 360. Thestresses and work hardening of the stock are I generally uniformthroughout the circumferential extent of the tubing thus formed and thetendency of the tube to unwrap, twist, or spiral is minimized oreliminated entirely.

In the drawings:

FIGURE 1 is a diagrammatic representation of a tube mill arranged toutilize the present invention.

FIGURE 2 is a composite partially diagrammatic elevational viewillustrating the conformation of the strip stock in various early stagesof its formation.

FIGURES 3, 4, and 5 are sectional views illustrating conditions of thestrip metal stock during further progressive stages of its formation.

FIGURES 6 and 7 are sectional views illustrating the final stages offorming the tube and illustrating the tube as being passed over amandrel.

Shown in FIGURE 1 is a tube mill 10 which may be of a generallyconventional type and which draws fiat strip metal stock 11 from a coil12 and passes the stock through a series of forming rolls to fashion thestock transversely to form tubing 13 which is then passed through asuitable furnace or heater 14 for heating the tubing and sealing orbonding its interfaces. The tubing is then passed through a cooler suchas a water jacket 15 from which it emerges as completed basic tube 16.Tube mill 10 is shown as including a number of sets of verticallyaligned forming rolls 2024, a series of horizontally aligned formingrolls 25-31, and two sets of finishing rolls 32 and 33. It will beunderstood that this arrangement of rolls is illustrative only and thatthe rolls can be arranged in any desired manner according to the requirements of the particular tubing being rolled. In some cases, a mandrel 35is utilized in the tube interior between finishing rolls 32 and 33. Thismandrel is anchored through a long rod 36 inserted into the partiallyformed tube as at 37 before the tubular form is closed.

The first set of rolls 20 bevels the edge portions of the stock inopposite directions as at 39 and 40 for a purpose to be described.Portions 41 and 42 of the strip adjacent opposite edges thereof are thenfashioned transversely counter-clockwise and clockwise respectively asthe drawings are viewed through about on radii of curvature whichclosely approximate the radii which they will have in the tubing to beformed. In some instances, the radii of portions 41 and 42 may be thesame and in other cases they may be slightly different to facilitatewrapping one longitudinal half of the strip around the otherlongitudinal half and to facilitate the latter forming stages in makingthe tube. This step may be accomplished at vertical rolls 21 and it willbe noted that the portions 43 and 44 of the strip lying between thelongitudinal central portion 45 thereof and the curved edges remaingenerally flat.

As the strip passes through vertical rolls 22, 23, and 24, intermediateportions 43 and 44 of the strip are fashioned transversely onprogressively diminishing radii of curvature which are greater than theradius of the initial radii at portions 41 and 42. Portions 43 and 44are formed respectively counterclockwise and clockwise to bring the sideedges of the strip stock toward each other and the changing radii ofthese portions of the stock are represented in FIGURE 2 generally at43a-c and 44a-c. The radii of portions 41 and 42 remain generallyunchanged during the forming of portions 43 and 44, though there may besome variation in shape resulting from the stresses in thestrip set upby this fashioning of the strip.

The strip then passes throughhorizontal rolls 25 and 26 whereintermediate portions 43 and 44 of the strip are further transverselyfashioned so that the strip assumes generally tubular form with the sideedges of the strip intersecting a common plane P as represented inFIGURE 2. Intermediate portions 43 and 44 have been formed on radii ofcurvature which are sufiiciently unlike to cause portion 42 to lieradially outwardly of portion 41 by at least the thickness of a sideedge of the strip so that upon continued rolling portion 42 will overlapportion 41.

In rolling the stock from its flat condition to the generally tubularcondition illustrated by the last stage of FIGURE 2, the curved portionsof the strip lying on opposite sides of the longitudinal centralportions 45 have provided abutments for suppotring the strip against thelateral forming pressures applied to the opposite half of the strip.

The strip is then passed through horizontal rolls 27 and 28 in whichportion 42 of the stock is lapped over the exterior of portion 41 andintermediate portions 43 and 44 of the stock are further formedtransversely so that the longitudinal halves of the stock on oppositesides of the longitudinal central portion 45 begin to wrap mutuallyaround each other. The half containing portions 41 and 43 of the stockconforms generally to the interior of the half containing portions 42and 44 while the latter half conforms generally to the exterior surfacesof the half containing portions 41 and 43. The condition of the stock atthis time is illustrated generally in FIG- URE 3; It will be noted thatthe stock has been provided adjacent its longitudinal central portionwith a step 46 for a purpose to be described. This step may be providedat any convenient stage in formation of the tube such as at verticalrolls 22.

As the partially formed tube passes through horizontal rolls 29 and 30,the radii of curvature of the outer and inner halves are progressivelydiminished so that the halves continue to wrap mutually to each other asillustrated in FIGURES 4 and 5. The tube is then passed throughhorizontal roll 31 where the halves are further wrapped and diminishedin radius to bring bevels 39 and 40 into close proximity'to oppositefaces of stepped portion 46. The tube is passed through finishing rolls32 and 33 which further constrict the wrapped halves to set the bevelson the step as illustrated in FIGURE 7. As pointed out, it may beadvantageous touse an internal mandrel in conjunction with the finishingrolls though a mandrel may not in all cases be necessary.

In the stages illustrated in FIGURES 35, portions 41 and 42 tend toretain their original radii of curvature but may change somewhat inshape because of stresses in the stock incident to the wrapping. Inparticular, outer portion 42 may be stressed to somewhat flattercondition in the intermediate stages (FIGURE 4) but this portion springsback and tends toresurne its original radius in the latter stages(FIGURE 6) to facilitate relatively snug wrapping of the outer plyaround the inner.

In the latter forming stages as well as in the earlie forming stages,curved portions of the stock on one side of the tubular form provideabutments for supporting the stock against lateral forming pressuresapplied to the opposite side. Both the inner half and the outer half ofthe stock are rolled through about 360 and the rolling is so nearlysymmetrical that the stresses set up in the longitudinal halves of thestock are substantially similar. The fact that the inner ply is formedon a slightly smaller radius of curvature than the outer ply does notgive rise to objectionable difference in stresses.

The tendency of the inner ply to spring back radially outwardly and theresistance thereto by the 'outer ply tends to hold the plies in snuguniform' interfacial engagement when the tube emerges from tube millThere is little'or no tendency for the tube to unwrap. The seam at theinterfaces of bevels 39, 40 and step 46 is generally uniform along thelength .of the tubing.

Since the stresses throughout circumferential portions of the tube areuniform, there is little or no tendency for it to twist or spiral.

These factors minimize the pressures required at the region of finishingrolls 32 and 33 and if a mandrel 35 is used, it has very long life, thusminimizing the man hours and tube mill hours lost in mandrelreplacement. Moreover, since the portions of the tube which engage themandrel are generally uniformly work hardened, there is little or nouneven wear on the mandrel. More generally, the symmetrical rolling ofthe various circumferential portions of the tube facilitates gradual,generally equal deformation of all circumferential portions of the tubestock and makes roll forming of the tube relatively trouble free.

One example of tubing made by the present method is as follows: Thestrip stock is of a relatively low carbon steel .014" thick and 2.250"wide. This stock is rolled to a two-ply tubular form having a outerdiameter and a wall thickness of .028. It has been found byexperimentation that in forming tubing by the present invention thestock stretches circumferentially about .050 less than the stockstretches utilizing the Woeller method discussed above.

The present invention makes it possible to roll tubing having heavier orthicker walls than was possible with prior methods. One reason for thisis that the present method employs no abrupt bends of the stock duringthe rolling which must subsequently be ironed out. Methods utilizing theabrupt bending and ironing out feature can not feasiably be used to rollthick materials to form thick walled tubing because as a practicalmatter it is too diflicult to iron out these sharp bends and then wrapthe work hardened, ironed out portions around the inner ply.

Another advantage of the present invention is that a tube mill utilizingthe invention can handle stock having greater tolerances of thicknessand temper than was possible by mills utilizing prior methods. Thisdecreases the machine and man hours spent inefiecting proper adjustmentsto handle different batches of stock.

We claim:

1. The method of forming tubing which comprises, moving a strip of metalstock lengthwise and while so moving said strip, fashioning a portion ofa longitudinal half of said strip on one side of the longitudinalcentral portion thereof transversely in a clockwise direction and on aradius of curvature closely approximating the radius which it will havein the tubing to be formed, fashioning a portion of the longitudinalhalf lying on the other side of said central portion of said striptransversely in a counterclockwise direction and on a radius ofcurvature closely approximating the radius which it will have in thetubing to be formed, fashioning other portions of said longitudinalhalves respectively in a clockwise and counterclockwise direction and onradii of curvature which are larger than the first mentioned radii ofcurvature to bring the side edges of the strip toward each other,lapping the side edge of one longitudinal half over the side edge of theother half, then, while leaving the first mentioned radii of curvaturesubstantially unchanged, fashioning said other portions of said onelongitudinal half on predetermined progressively diminishing radii ofcurvature, and simultaneously therewith, fashioning said other portionsof the other longitudinal half transversely on slightly smallerprogressively diminishing radii of curvature so that said first halfoverlies and generally conforms to the curvature of said other half, andcontinuing so to fashion said other portions of said halves until saidedges are adjacent opposite faces of said longitudinal central portion.

2. The method of forming tubing which comprises, moving a strip of metalstock lengthwise and while so moving said strip, fashioning a portion ofa longitudinal half of said strip lying a predetermined distancelaterally of the longitudinal central portion thereof transversely in aclockwise direction and on a radius of curvature which closelyapproximates the radius which it will have in the tubing to be formed,fashioning a portion of the longitudinal half lying generally an equaltransverse distance on the opposite side of said central portion of saidstrip in a counterclockwise direction and on a radius of curvatureclosely approximating the radius which it will have in the tubing to beformed, fashioning portions of said halves lying intermediate the firstmentioned portions thereof respectively in a clockwise andcounterclockwise direction on radii of curvature which are larger thanthe first mentioned radii of curvature and which are dilferent from eachother, thereby bringing the side edges of the strip toward each otherwith the side edge of one of said halves lying radially outwardly of theside edge of the other half, then, while leaving the first mentionedradii of curvature substantially unchanged, fashioning the intermediateportions of said one longitudinal half transversely on predeterminedprogressively diminishing radii of curvature, and simultaneouslytherewith, fashioning the intermediate portions of said otherlongitudinal half on slightly smaller progressively diminishing radii ofcurvature so that the said first half overlaps and generally conforms tothe curvature of the exterior of said other half, and continuing so tofashion said intermediate portions of said halves until said side edgesare adjacent opposite faces of said longitudinal central portion.

3. The method of forming tubing which comprises, moving a strip of metalstock lengthwise and while so moving said strip, fashioning a portion ofsaid strip lying adjacent one side edge thereof transversely in aclockwise direction and on a radius of curvature closely approximatingthe radius which it will have in the tubing to be formed, fashioning aportion of said strip lying adjacent the other side edge transversely ina counterclockwise direction and on a radius of curvature closelyapproximating the radius which it will have in the tubing to be formed,fashioning the portions of said strip lying between the first mentionedportions thereof respectively in a clockwise and counterclockwisedirection on radii of curvature which are greater than the firstmentioned radii and thereby bringing the side edges of said strip towaadeach other, lapping one of said side edges over the other, then, whileleaving the first mentioned radii of curvature substantially unchanged,simultaneously fashioning said intermediate portions of said striptransversely on predetermined progressively diminishing radii such thatone longitudinal half of the strip overlaps and generally conforms tothe curvature of the exterior of the other half, and continuing so tofashion said halves until said edges are adjacent opposite faces of saidlongitudinal central portion.

4. The method of forming tubing which comprises, moving a strip of metalstock lengthwise and while so moving said strip, transversely fashioningportions of said strip adjacent its side edges respectively clockwiseand counterclockwise through about 90 on radii of curvature closelyapproximating the radii which they will have in the tubing to be formed,then transversely fashioning intermediate portions of said striprespectively clockwise and counterclockwise on radii of curvature whichare initially greater than the first mentioned radii, and there bybringing said side edges toward each other, lapping one side edge overthe other, and While leaving the first mentioned radii of curvatureunchanged, simultaneously fashioning said intermediate portionstransversely on progressive diminishing radii of curvature until saidside edges lie adjacent opposite faces of a generally centrallongitudinal portion of said stock,

5. In a method of forming tubing by fashioning strip stock to tubularform while the strip is moved lengthwise, the improvement whichcomprises, first fashioning edge portions of the strip respectivelyclockwise and counterclockwise on radii of curvature closelyapproximating the radii which they will have in the tube to be formed,then, without changing substantially said radii,

fashioning intermediate portions of said strip respectively clockwiseand counterclockwise on radii of curvature initially larger than thefirst mentioned radii and progressively diminishing, lapping one sideedge of said strip over the other, and simultaneously continuing so tofashion said intermediate portions until the radii thereof arediminished substantially to the radius of said tube and said side edgesare disposed adjacent opposite face portions of the longitudinal centralportion of said strip.

6. The method of forming tubing which comprises, moving a strip of metallengthwise and while so moving said strip applying to longitudinalhalves of said strip on opposite sides of the longitudinal centralportion thereof lateral forming pressure, controlling said pressure sothat the portions of said halves adjacent their free edges are fashionedtransversely in clockwise and counterclockwise directions respectivelyon radii of curvature closely approximating the radii which they willhave in the tubing to be formed, then applying further transverseforming pressure to said halves and controlling the latter said formingpressure so that the portions of said halves intermediate said edgeportions and central portion transversely fashioned in clockwise andcounterclockwise directions respectively on radii of curvature largerthan the first mentioned radii, lapping the side edge of one halfoutside of the side edge of the other half, simultaneously applyingfurther lateral forming pressure to said intermediate portions of saidlongituidnal halves while leaving the first mentioned radii of curvaturesubstantially unchanged, controlling the latter said pressure so thatsaid halves wrap simultaneously relative to each other with said onehalf conforming generally to the exterior surface of said other half andsaid other half conforming generally to the interior surface of said onehalf, and continuing the latter said forming pressure until said sideedges are disposed adjacent opposite faces of said longitudinal centralportion.

7. The method defined in claim 5 wherein said edge portions of saidstrip are fashioned on radii of curvature which are substantially equal.

8. The method of forming tubing which comprises, moving a strip of metalstock lengthwise and while so moving said strip, fashioning indirections respectively clockwise and counterclockwise and on radii ofcurvature closely approximately their radii in the tubing to be formed,portions of said strip spaced in opposite directions from thelongitudinal central portion of said strip and thereby bringing theedges of said strip toward each other, further bringing said edgestoward each other by fashioning others of said portions respectivelyclockwise and. counterclockwise on radii of curvature larger than thefirst mentioned radii, lapping the side edge of onehalf of said stripover the side edge of the other half, and, while leaving the firstmentioned radii of curvature substantially unchanged, further andsimultaneously fashioning said other portions of the longitudinal halvesclockwise and counterclockwise respectively on progressively diminishingradii with the radius of curvature of said onehalf being slightlygreater than the radius of curvature of the other half so that saidone-half overlaps and generally conforms to the curvature of theexterior of the other half, and continuing so to fashion said otherportions of said halves until said side edges are adjacent oppositefaces of said longitudinal central portion.

9. The method of forming tubing which comprises, providing a strip ofsubstantially flat metal stock, moving the strip lengthwise, and whileleaving the longitudinal central region of said strip substantially flatfashioning portions of said strip adjacent its edges respectivelyclockwise and counterclockwise on radii of curvature closelyapproximating the radii which they will have in the tubing to be formed,then while leaving said radii substantially unchanged fashioningportions of said central region respectively clockwise andcounterclockwise on radii of curvature which are larger than the firstmentioned radii of curvature to bring the side edges of the strip towardeach other, lapping one of said side edges over the other, then whileleaving the first mentioned radii of'curvature substantially unchangedsimultaneously continuing so to fashion said portions of said centralregion until the radii thereof are diminished substantially to thedimensions of said tube and said side edges are disposed adjacentopposite face portions of the longitudinal central portion of saidstrip.

References Cited in the file of this patent UNITED STATES PATENTSMcCloud "Jan. 12, 1909 Bundy Dec. 11, 1923 Quarnstrom Apr. 28, 1936Quarnstrom Mar. 11, 1941 Woeller Aug. 11, 1942

